Background/Purpose: Enthesitis affects approximately a third of patients with psoriatic arthritis (PsA) and is often considered the earliest site of inflammation. The accuracy of clinical examination of enthesitis is limited. Ultrasound could improve detection of enthesitis, however, there is no accepted score for assessment of sonographic enthesitis in PsA. The objective of this study is to assess the performance of various sonographic elemental entheseal lesions in distinguishing between PsA and healthy controls which will inform the development of a novel sonographic enthesitis score for PsA.

Methods: A total of 100 age- and sex-matched individuals (50 PsA and 50 controls) were recruited for this cross-sectional study. Patients with PsA were recruited during their clinic visits. Healthy controls with no personal or family history of inflammatory arthritis were recruited from hospital personnel and advertisements. Eleven entheseal sites were scanned bilaterally according to a standardized protocol by two sonographers. The selection of entheseal sites for this study was based on systematic literature review and expert opinion of rheumatologists experienced in musculoskeletal ultrasound in PsA. Based on OMERACT definition of sonographic enthesitis, the following lesions were assessed: structural changes, thickness, erosion, enthesophytes, calcification, power Doppler (PD) signal, bursitis, and bone irregularities. The images were read by two readers blinded to the clinical information. The intra- and inter-rater reliability for scoring the lesions was excellent (ICC 0.92 to 0.96). Chi square tests were used to compare the frequency of the various lesions between PsA and controls. The sensitivity, specificity and positive predictive value (PPV) of entheseal lesions were computed.

Results: Mean age was 55 ± 10 years, 59% were males, average BMI was 29, and average disease duration was 14.6 years. The frequencies of the various entheseal lesions and their ability to distinguish between PsA and controls are presented in Table 1. The lesions that had the highest PPV were: PD at the enthesis (PD grade greater than 2 (100%) and PD grade greater than 1 (97%)), erosions (89%) and bone proliferation (87%). In general, the sensitivity of was much lower ranging from 0.1% to 27%. No significant differences were found in the frequencies of calcifications or bursitis between PsA patients and controls.

Conclusion: We identified elemental ultrasonographic abnormalities that could distinguish PsA and controls. This information will contribute to the development of a new sonographic score for assessment of enthesitis in patients with PsA that could be used for diagnostic purposes and contribute to new understanding and clinical application of ultrasonographic enthesitis at the bedside.